THE SEXSORLVL FUNCTIOX. 



1.53 



with respiration or breathing. The act of bi^eathing is essential to Hfo, 

 and were it to cease, the animal would die. These are nerves of involun- 

 tary motion ; so 

 that, whether he 

 is awake or asleep, 

 conscious of it or 

 not, the lungs 

 heave and life is 

 supported. Lastly, 

 extending from 

 the medulla ob- 

 longata is the 

 spinal cord — a 

 further prolonga- 

 tion of the brain, 



running through a cavity in the bones of the neck, back, and loins, and 

 extending to the sacral canal — from which other nerves ai-e given off at 

 certain intervals. This cut delineates a pair of them. The portion of 

 spinal cord represented, is supposed to be placed with its inner or lower 

 surface towards us. The spinal cord, «, is composed of six distinct 

 divisions or rods, running- throuo-h its whole length — three on either side. 



rm . . . ^ 



ihe two upper divisions pi'oceed from those tracks of the brain devoted to 

 sensation. Numerous distinct fibres spring abruptly from the column, and 

 which collect together, and, developing a little ganglion or enlargement, 

 d — an enlargement of a nervous cord is called a ganglion — become a nerve 

 of sensation. From the lower or inner side — a prolongation of the track 

 devoted to motion — proceed other fibres, which also collect gradually 

 together, and form a nervous cord, c, giving the power of motion. Beyond 

 the ganglion the two unite, and form a perfect spinal nerve, h, possessing 

 the power both of sensation and motion ; and the fibres of the two columns 

 proceed to their destination, enveloped in the same sheath, and apparently 

 one nerve. Each portion, however, continues to be wrapped in its own 

 membrane. They are united, yet distinct ; they constitute one nerve, yet 

 neither their substance nor their office is confounded. Our cut, closely 

 examined, will give at h some idea of the manner in which these distinct 

 fibres are continued ; — each covered by its own membrane but all enveloped 

 in a common envelope. The difference of action in the sentient and motive 

 portions of the nerves must not be lost sight of; in the sentient, the im- 

 pression commences in the minute ramifications of the nerve, and is carried 

 on through the ti^unk to the sensorium : while, on the contrary, in the 

 motor, the volition originates in the brain itself, and is communicated to 

 the muscles ; the impression in the sentient nerves traversing from the 

 tissues to the brain, and m the motor from the brain to the tissues. 



All these nerves are organs of sensation and motion alone ; but there 

 are others whose origin seems to be outside of and below the brain. These 

 are the s)jrnpatJiefic, so called from their union and sympathy with all the 

 others, and identified Avith life itself. They arise from a small enlargement, 

 called the anteinor cervical ganglia, in the upper part of the neck, and are 

 more or less distributed over every part of the body. They go to the heart, 

 and its beats : and to the stomach, and it digests. They form a network 

 round each blood-vessel, and the current flows on. Tliey surround the 

 very minutest vessels, and the frame is nourished and built up. They arc 

 destitute of sensation, and they are perfectly beyond the control of the will. 



The reader, we trust, will now comprehend this wonderful yet simple 

 machinery, and be able, by-and-by, to refer to it the explanation of several 

 diseases, and particularly of the operation to which wc have i-eferred. 



